ChargetransferWiderstand

Charge transfer resistance, commonly denoted Rct, is a parameter in electrochemistry that quantifies the resistance to electron transfer across the electrode–electrolyte interface during redox reactions. In electrochemical impedance spectroscopy (EIS), Rct is associated with the kinetic barrier to charge transfer and is often visualized as the diameter of the semicircular feature in a Nyquist plot at mid frequencies.

In a standard Randles-type circuit, the elements include the solution resistance (Rs), the charge transfer resistance (Rct), the double-layer capacitance (Cdl) or a constant phase element, and a Warburg impedance representing diffusion. The magnitude of Rct reflects the ease of interfacial electron transfer: smaller values indicate faster kinetics, while larger values imply sluggish charge transfer.

Rct can be determined by fitting impedance data to an equivalent circuit, or, in ideal cases, by measuring the semicircle diameter in the Nyquist plot. Non-ideal behavior is often modeled with a constant phase element to account for surface heterogeneity or distributed time constants. Rct may also be expressed per unit area as Ω·cm^2 when normalized to the electrode surface.

Factors influencing Rct include electrode material and surface morphology, catalyst presence, electrolyte composition and concentration, temperature, and the applied overpotential. Applications span corrosion studies, battery and supercapacitor research, fuel cells, sensing, and electroplating.